<h2>Problem 222</h2>
<div style="color:#666;font-size:80%;">19 December 2008</div><br />
<div class="problem_content">
<p>What is the length of the shortest pipe, of internal radius 50mm, that can fully contain 21 balls of radii 30mm, 31mm, ..., 50mm?</p>

<p>Give your answer in micrometres (10<img src="" style="display:none;" alt="^(" /><sup>-6</sup><img src="" style="display:none;" alt=")" /> m) rounded to the nearest integer.</p>
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